Welcome to the AAVSO
Long Period Variable Section!
AAVSO LPV Section Leaders:
Administrator: Andrew Pearce
Assistant Administrator: Michael Soukup
Science Advisors: Dr. Laszlo Kiss, Dr. John Percy,
Dr. Lee Anne Willson
Getting Started with the AAVSO LPV Section
September 2, 2014
Thank you for visiting the home of the Long Period Variables (LPV) Section! Whether you are an active observer (of LPVs or other variable star types) or are a newcomer curious about LPVs and the AAVSO in general (and perhaps thinking about participating in observing variable stars) we hope that you find these pages of use! A goal of ours is to continually improve the usefulness of these pages to LPV observers and to stimulate continued interest in LPVs.
The AAVSO intends for the LPV Section to encourage the observation (whether by visual means or CCD/photoelectric photometry) of LPVs, to serve as a resource clearing house for LPV related science and information for observers, and to serve as a social hub for members of the extended AAVSO community interested in the science and observation of LPVs.
When we say "LPVs" we are not referring to a specific type of variable star, but rather to a large and diverse group of different types that we have chosen to place under the LPV umbrella. We choose to limit variable star types as LPV members to those whose brightness changes are due to pulsation and with periods (or approximate periods) longer than some dozens of days, up to periods of around 1000 days. Thus, Cepheid, RR Lyrae, and delta Scuti variables are pulsators, but their periods are too short to be included as LPVs. And, we do not include eclipsing binaries or eruptive-type variables, along with many other kinds of variables.
Even so, what we include as LPVs make up quite a few kinds of pulsating stars in terms of spectral type, stellar mass, and stage of evolution. Classification, for some, is difficult, either because the star in question has not been well observed, or some physical characteristic of the object is at odds with what most of the other stars placed in the same "box" have, such as stellar mass. We suggest you read the articles describing the LPV Zoo (found by following the link provided to the upper left on this page). These articles present the "official" descriptions (given in the General Catalog of Variable Stars, the internationally accepted clearinghouse for variable star types and cataloging) of the variables we include as LPVs, and additional information that helps enhance the official descriptions. There are LPV types that will interest almost anyone!
Our "bread and butter" LPVs are the "Miras", named after the prototype omicron Ceti, or "Mira The Wonderful". Mira was known to a number of ancient cultures, e.g., the Arabs and the Greeks, as a variable star. Miras are typically lower mass stars that are in the red giant phase of their evolution. The light curves for many look stable over years of observation, yet continued observation by the AAVSO and other variable star organizations has shown more than a few to be changing their periodicity, as well as exhibiting some unusual behavior in their light curves! These changes are indicative of the evolutionary processes taking place within the stars. Yes, these changes are slow to detect in any person's lifetime, but detecting these changes makes these stars scientifically important, and validates the continued observation of them over a long time span. We also include the semi-regular red giant pulsators, the SRa and SRb types. These LPVs exhibit less regular (periodic) light curves than do Miras, presumably because these are in a somewhat different evolutionary stage in their lives. Again, studying their light curves has revealed some to be showing noteworthy behavior. More observations over long time periods are essential, as for Miras.
Then we have the SRc LPVs. These are believed to be massive stars that are in the red (super)-giant phase of their lives, probably on the way to eventually becoming supernovae. These stars tend to have longer, but less periodic, light curves than the Miras and semiregulars. These are rare stars. Some have low amplitude brightness ranges ( <= 1 magnitude) while other have ranges of several or more magnitudes, making these latter stars easy to observe by visual means.
We also include the "L" types of variables. These are variables that have poorly defined periodicity of brightness changes. Indeed, some may not truly be variables at all. Others may just have not been observed enough to determine if they actually belong in one of the categories mentioned above. The L types include red giants and supergiants.
Another LPV group comprises the RV Tauri variables. These are yellow supergiants in a later stage of evolution than the red giants. They are believed to be low mass stars, perhaps not much more than our Sun's mass. They exhibit unique light curves. Some light curves tend to be quite regular, with others showing a bit less regular curve and a superimposed "wave" of a longer periodicity. Hence, the subtypes of RVa and RVb. These variables have periods ranging from dozens of days to 100 or so days, notably shorter than the Miras and semi-regulars. These are also rare stars because they are believed to represent a very short lived evolutionary phase in their overall lives. Stellar evolution here is at a fast pace! Continual observation of the RV Tauris will likely reveal some interesting aspects of these objects.
Then we have the SRd LPVs. This is a bit of a mixed bag of pulsating variables. Most are thought to be low mass stars and in a late giant or supergiant stage of their lives. Their spectral types are typically F, G, or K, much like the RV Tauris. It is currently thought that these two types are related, each being in a somewhat different evolutionary stage. Here again, continued observation of the SRd and RV Tauri types may shed more light as to how these stars are related and to the details of late stellar evolution of low mass stars.
We mentioned that the SRds include a few unusual stars, not readily placed elsewhere. The massive yellow hypergiant, rho Cas, is a good example of one. It is a pulsator (similar to much lower mass SRd variables), and of low amplitude usually. However, over years on an irregular basis, it exhibits spells of considerable brightness increases. Such stars are of very high mass and thus are very rapidly evolving, likely to ending their lives as supernovae. rho Cas is always worthy of observing whether by visual or electronic means!
The great majority of the LPVs described above in the AAVSO program have brightness amplitude changes that readily allow for accurate visual observation and brightness estimates. And, of course, all are accessible for photoelectric and CCD photometry measurements.
We encourage everyone to spend some time with the page links given to the left. These pages provide a good overview of what the LPV Section is about.
Please browse the site to learn more about LPVs and how your observations will help science uncover more about these important variable stars.
Noise Characteristics of Long-Term Visual Light Curves
by Matthew Templeton and Margarita Karovska
January 23, 2013
Red noise, incoherent variations that exhibit stronger power at lower frequencies, are observed in a number of astrophysical phenomena. (See Kiss, Szabo, & Bedding 2006, and Templeton & Karovska 2009 for examples in AGB and supergiant stars; see Uttley, McHardy, & Papadakis (2002) and Rothschild et al. (2011) for examples from AGN. This noise manifests itself in observational data as a power-law underlying any periodic signals. The character of this noise seems to have broadly similar properties for variability in different types of object but there is no clear pattern in the character of red noise as a function of other properties (e.g. spectral type, pulsation period, or other stellar characteristics). Our aim in this study is to explore the parameter space of both stellar properties and data properties, and determine whether any of these relate to the observed power law spectra in Mira variables, or any other class of variable star for which the AAVSO has visual data. We discuss the power spectral properties of large samples of Mira variables from the AAVSO International Database, along with smaller samples of other variable star classes.
Presented at the 221st AAS Meeting in Long Beach, CA, January 9, 2013
by Lee Anne Willson and Massimo Morengo
July 18, 2012
Mira variables share essential characteristics: High visual amplitude, periods of hundreds of days, red colors (spectral types M, S, and C), and the presence of emission lines at some phases. They are fundamental mode pulsators, with progenitor masses ranging from >1 to several solar masses. In this review, we summarize what is known from modeling and observational studies, including recent measurements from optical and IR interferometry, and studies involving large samples of stars particularly in the Magellanic Clouds. While we have a good idea of how these stars fit into the big picture of stellar evolution, many important details remain to be settled by a combination of more ambitious models and new observational techniques. Carrying on observations of bright Mira variables will be essential for interpreting observations of large numbers of fainter sources as well as for assessing the completeness and accuracy of the models.
Quarterly Data Reports now in the AAVSO Newsletter
January 23, 2013
Starting with the October 2012 Newsletter, we started a column that listed the most- and least-observed stars in both the AAVSO LPV and CV Legacy programs as a means of highlighting what stars in these two key lists were and were not getting good coverage. We've repeated this with "Looking at Legacy Stars" in the January 2013 Newsletter (see page 21). We encourage you to refer to this column in your seasonal planning. You should also look through the full LPV Program and Legacy LPV, and Binocular Program lists to see which stars are right for you and worth adding to your observing program. Don't forget, we also have the AAVSO Basic Observation Planner available on the AAVSO website as well!
Check out the LPV Discussion Forum on the AAVSO Website!
There is now a discussion forum on the AAVSO website dealing with LPVs and related topics. Drop in to see what observers and researchers are talking about, ask questions and share your experiences and knowledge.
Telescopic LPVs for New Visual Observers
Okay, so you’ve been observing some naked eye and binocular variables for a while. Good for you! The stars in the AAVSO Ten Star Training Program can be fun and rewarding to observe for a lifetime.
Maybe you were drawn in by the Citizen Sky project and now you’re getting hooked on variable stars. Hey, it happens; you are not alone. But epsilon Aurigae is in full eclipse now, and will remain faint for most of this year, so maybe you’re ready for some new stars to satisfy your new addiction.
Perhaps you already owned a telescope or you finally got that shiny new 8” Schmidt-Cassegrain you’ve had your eye on for Christmas. Now where do you look for interesting variables? I’ve got some suggestions for you. These are fun stars to observe, AAVSO still needs observations of these stars, and best of all, they are easy to find and identify, so you won’t spend cold winter nights looking for them. You can spend your time observing them instead!
Read the full story
Interesting Behavior of a Carbon Star Mira, CT Lacertae
October 8, 2014
AAVSO's Science Director, Dr. Matthew Templeton and his co-authors, all AAVSO LPV observers, have recently published an interesting preprint for the eJAAVSO Journal on the long term magnitude amplitude changes of a Mira-type pulsator, that is also a well known carbon star of late spectral type.
"CT Lacertae: Another Long-period Carbon Star with Long-timescale Variations" (Templeton et. al.) is found here for your reading.
Although not as extensively observed over the many years since its discovery as a variable in 1935 as other Mira-type LPVs there is enough data to show this star is definitely exhibiting changes in its evolution as a red giant. In particular, although there looks to be little change in the star's light curve periodicity, its amplitude range in magnitude has decreased by about two magnitudes! This behavior has been observed in other LPVs, too. Will CT Lac eventually return to its former amplitude range? Or will it decrease even further? We do not know. Only continued observation will tell us. But what we are seeing here, thanks to the dedicated observers of the AAVSO and other variable star organizations over the long haul is evidence of stellar evolution on a time scale we can see. CT Lac is a good example of why continued, long term observations of LPVs is most important.
The paper also presents a detailed time series analysis of CT Lac's light curve, revealing possible evidence of multi-mode pulsation. This is fascinating stuff for those interested in the analysis of light curves, and what it reveals about a star's evolution in the late stages of its life! And the best analysis depends on acquiring a lot of data over a long period of time!
My Favorite Double Star
Mike Simonsen (SXN)
If you have spent any time looking through binoculars or telescopes you have undoubtedly come across a double star or two. Someone probably showed you Albireo (beta Cygni) at a star party or tried to impress you with a view of epsilon Lyrae, the famous Double Double in Lyra. One of my favorites is Rigel, the lower foot of Orion. Not many observers know Rigel is actually a double star. It has a 6.8 magnitude companion, Rigel B, 9 arc seconds away. This would be an easy double to separate in most small telescopes, but Rigel is the seventh brightest star in the sky. As such, it is some 400 times brighter than its companion, so Rigel B gets lost in the glare of its primary. Once you know where to look it's easy to find.
Double stars are interesting to people for a number of reasons. Some like the challenge of splitting close pairs with the smallest instrument possible. Others like to measure the characteristics, such as separation, position angle and magnitudes. But what really delights most people is a pair that exhibits a striking color combination. Some of the more popular pairs include Alberio (gold/sapphire), gamma Andromedae (gold/blue), xi Bootis (yellow/red) and alpha Herculis (red/green). I don't want to get into a debate about the perceived colors of these pairs. Your mileage may vary.
My favorite double has them all beat. It is a very colorful pair, with a blue-white primary and a deep red secondary. But the best part is this. It looks different every time you look at it, because the deep red secondary is a variable star! That's right, my favorite double star is also a variable.
You knew that was coming, right?
Okay, okay, I'll end the suspense. My favorite double is the Mira variable T Draconis.
The faint stars in the comparison star sequence for T Draconis
The Biggest Star in the Universe
by Bob King
Astronomy is full of superlatives. Farthest, closest, hottest, densest, biggest, smallest. It’s fun to prowl around the sky in search of these extremes.
Two nights ago, I found myself star-hopping across Canis Major the Greater Dog in search of this or that gas cloud and spotted the star VY Canis Majoris on my atlas. The use of the lettered name “VY” tells us first off that this is a variable star whose light is not constant like the sun’s.
A quick check on the American Association of Variable Star Observers (AAVSO) website shows that VY varies between magnitudes 7.4 at brightest to 9.6. For the past few months it’s been around 8.0, bright enough to see in ordinary binoculars.
But its variability is not exactly the reason I wanted to acquaint you with this star. VY is special for an entirely different reason – it’s the largest star known! Astronomers estimate its diameter at some 2,000 times the size of the sun. And since the sun is no slouch at 864,000 miles across, VY is truly a monster.